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[Discuss-gnuradio] Distorted Spectrum after applying gr.freq_xlating_fir

From: Bruhtesfa Ebrahim
Subject: [Discuss-gnuradio] Distorted Spectrum after applying gr.freq_xlating_fir_filter_ccc
Date: Mon, 19 Jan 2009 11:46:22 +0100

Hey all,
 I transmit a carrier at 2.45GHz using one USRP and recieve using another USRP as it is required for my application.
But the spectrum i get has a frequency offset of about 7.68KHz as shown in the attached file.
So, I used gr.freq_xlating_fir_filter after usrp_source to demodulate the signal to baseband (based on the advice by Micheal Dickens,thank you by the way).
However, the signal spectrum I got is not exactly at zero, it is around 320Hz.
Moreover, the spectrum is too distorted as shown in the 2nd figure attached.
So, can this distortion be removed using the parameters or is there some other solution?
- The sampling rate of the original recieved signal from USRP was 64MHz/128=500KHz, so I used decimation factor of 500 in the xlating filter such that the output baseband signal will have a sampling rate of 500KHz/500=1KHz.
-  since the frequency offset of the signal in 1st figure is -7.68KHz, i used the opposite freq_offset=7680 in the xlating filter.
- i used cut off frequency =500Hz and width of transition band=200Hz.

Attachment: freq_shift_before_xlating.jpg
Description: JPEG image

Attachment: freq_shift_after_xlating.jpg
Description: JPEG image

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